It appears like the clojure compiler doesn't get the starting scope of let bindings right from the java debug interface perspective.

The compiler sets the starting scope of a local to the let/loop body, rather than to immediately after the local is bound. So when you are stepping through a let statement in a debugger, you can't eval the already defined bindings until you get to the let body.

Because it is a compiler problem, you see the symptoms with any jdi based debugger, (I've confirmed this on both jdb and cdt.)

The fix is pretty straightforward. Just gen.mark() a label after each binding is emitted and use that in the gen.visitLocalVariable() call instead of the loopLabel. I've attached a patch for clojure 1.2 branch. (If there is interest I'll create one for clojure master.)